We report water vapor sorption studies on four primitive cubic, pcu, pillared square grid materials: SIFSIX-1-Cu, SIFSIX-2-Cu-i, SIFSIX-3-Ni, and SIFSIX-14-Cu-i. SIFSIX-1-Cu, SIFSIX-3-Ni, and ...SIFSIX-14-Cu-i were observed to exhibit negative water vapor adsorption at ca. 40–50% relative humidity (RH). The negative adsorption is attributed to a water-induced phase transformation from a porous pcu topology to nonporous sql and sql-c* topologies. Whereas the phase transformation of SIFSIX-1-Cu was found to be irreversible, SIFSIX-3-Ni could be regenerated by heating and can therefore be recycled. In contrast, SIFSIX-2-Cu-i, which is isostructural with SIFSIX-14-Cu-i, exhibited a type V isotherm and no phase change. SIFSIX-2-Cu-i was observed to retain both structure and gas sorption properties after prolonged exposure to heat and humidity. The hydrolytic stability of SIFSIX-2-Cu-i in comparison to its structural counterparts is attributed to structural features and therefore offers insight into the design of hydrolytically stable porous materials.
Purification of ethylene (C
H
), the largest-volume product of the chemical industry, currently involves energy-intensive processes such as chemisorption (CO
removal), catalytic hydrogenation (C
H
...conversion), and cryogenic distillation (C
H
separation). Although advanced physisorbent or membrane separation could lower the energy input, one-step removal of multiple impurities, especially trace impurities, has not been feasible. We introduce a synergistic sorbent separation method for the one-step production of polymer-grade C
H
from ternary (C
H
/C
H
/C
H
) or quaternary (CO
/C
H
/C
H
/C
H
) gas mixtures with a series of physisorbents in a packed-bed geometry. We synthesized ultraselective microporous metal-organic materials that were readily regenerated, including one that was selective for C
H
over CO
, C
H
, and C
H
.
The Government of India implemented a nationwide lockdown from March 24, 2020 in response to the Coronavirus disease (COVID-19) outbreak. This study examines the effects of two positive psychological ...resources on the mental health of Indian citizens during the early days of the lockdown. The effects of psychological capital (PsyCap) and internal locus of control on psychological distress of people via affect balance were tested. Data were collected through an online survey from 667 participants. Psychological distress was assessed using the GHQ-12, and affect balance was assessed as the preponderance of positive over negative affect. Results reveal that psychological capital and internal locus of control were negatively associated with psychological distress. In addition, affect balance mediated the relationship between psychological capital and psychological distress and the relationship between internal locus of control and psychological distress. Thus, both the psychological resources through affect balance acted as buffers protecting people from mental health deterioration during COVID-19 lockdown. However, the direct and indirect effects of psychological capital on psychological distress is stronger than that of internal locus of control. Implications and directions for future research are discussed.
Sequestration of CO2, either from gas mixtures or directly from air (direct air capture, DAC), could mitigate carbon emissions. Here five materials are investigated for their ability to adsorb CO2 ...directly from air and other gas mixtures. The sorbents studied are benchmark materials that encompass four types of porous material, one chemisorbent, TEPA‐SBA‐15 (amine‐modified mesoporous silica) and four physisorbents: Zeolite 13X (inorganic); HKUST‐1 and Mg‐MOF‐74/Mg‐dobdc (metal–organic frameworks, MOFs); SIFSIX‐3‐Ni, (hybrid ultramicroporous material). Temperature‐programmed desorption (TPD) experiments afforded information about the contents of each sorbent under equilibrium conditions and their ease of recycling. Accelerated stability tests addressed projected shelf‐life of the five sorbents. The four physisorbents were found to be capable of carbon capture from CO2‐rich gas mixtures, but competition and reaction with atmospheric moisture significantly reduced their DAC performance.
Five benchmark materials are investigated for their ability to adsorb CO2 directly from air. It is found that physisorbents can compete with chemisorbents with respect to CO2/N2 selectivity but direct air capture (DAC) performance is mitigated because of competition with water vapor. Optimizing pore size and pore chemistry in the presence of water vapor must be further addressed if physisorbents are to compete with chemisorbents.
Harnessing high-frequency spin dynamics in three-dimensional (3D) nanostructures may lead to paradigm-shifting, next-generation devices including high density spintronics and neuromorphic systems. ...Despite remarkable progress in fabrication, the measurement and interpretation of spin dynamics in complex 3D structures remain exceptionally challenging. Here, we take a first step and measure coherent spin waves within a 3D artificial spin ice (ASI) structure using Brillouin light scattering. The 3D-ASI was fabricated by using a combination of two-photon lithography and thermal evaporation. Two spin-wave modes were observed in the experiment whose frequencies showed nearly monotonic variation with the applied field strength. Numerical simulations qualitatively reproduced the observed modes. The simulated mode profiles revealed the collective nature of the modes extending throughout the complex network of nanowires while showing spatial quantization with varying mode quantization numbers. The study shows a well-defined means to explore high-frequency spin dynamics in complex 3D spintronic and magnonic structures.
Porous materials capable of selectively capturing CO2 from flue‐gases or natural gas are of interest in terms of rising atmospheric CO2 levels and methane purification. Size‐exclusive sieving of CO2 ...over CH4 and N2 has rarely been achieved. Herein we show that a crystal engineering approach to tuning of pore‐size in a coordination network, Cu(quinoline‐5‐carboxyate)2n (Qc‐5‐Cu) ena+bles ultra‐high selectivity for CO2 over N2 (SCN≈40 000) and CH4 (SCM≈3300). Qc‐5‐Cu‐sql‐β, a narrow pore polymorph of the square lattice (sql) coordination network Qc‐5‐Cu‐sql‐α, adsorbs CO2 while excluding both CH4 and N2. Experimental measurements and molecular modeling validate and explain the performance. Qc‐5‐Cu‐sql‐β is stable to moisture and its separation performance is unaffected by humidity.
Sieves you right: Crystal engineering of supramolecular isomers of Cu(quinoline‐5‐carboxyate)2n metal–organic materials enables the right pore‐chemistry for ultra‐high CO2/N2 and CO2/CH4 selectivity even in the presence of water vapor.
This study analyses regional drought characteristics (frequency, severity, and persistence) of meteorological droughts occurred in the northwestern parts falling under arid and semiarid regions of ...India with mean annual rainfall ranging between 100 and 900 mm. A drought is defined as a season or a year with rainfall less than 75% of corresponding mean at a place. Long-term monthly rainfall records (1901–2013) of 90 districts of north-west India located in the states of Punjab, Haryana, Rajasthan and Gujarat are used in the analysis. The percentage departure of seasonal rainfall from long-term average rainfall has been used for identification of onset, termination, and quantification of drought severity. The average frequency varied from once every 3–4 years. The westerly districts have an average drought return period of 3 years, while districts lying toward the east had droughts once every 4 years. Only four of the 90 districts in the study area experienced droughts once every 5 years. Persistent droughts of 2, 3, and 4 year duration occurred widely. Severe droughts occurred in the years 1904, 1905, 1911, 1918, 1931, 1939, 1985, 1986, 1987, 1993, and 2002, with an average frequency of severe drought events of one in 10 years. The analysis presented in this paper improves understanding of the regional drought characteristics and will inform drought mitigations and strategies in these arid and semiarid areas.
The synthetic origin of nanocarbon and its role on the luminescence properties of carbon nanodots, in particular, citric acid derived ones, remain an enigma to date. We report here, for the very ...first time, that citrazinic acid alone builds a nanocarbon structure upon incubation in dimethylformamide at room temperature. The emission properties of incubated fluorophore resemble that of a nanodot. The dispersion of the H-bonded cluster’s size originated from citrazinic acid only is the cause of excitation-dependent emission. We have shown that the steric hindrance caused by the presence of alkyl chain of butyl amine restricts such dispersions, resulting in excitation-independent emission, a molecular behavior. On the other hand, for achieving white-light emission through a one-step method, the solvothermal reaction of citric acid with ammonium thiocyanate has been performed. The ground-state heterogeneity and luminescence properties are strongly influenced by the solvent polarity. We identify the existence of blue-, green-, and red-emissive fluorophores in a product obtained from solvothermal reaction. The computed vertical excitations of the molecular fluorophore predicted by the reaction mechanism are in good agreement with the experimental observations. Unprecedently, a product-embedded PVA/PVP film exhibits white light emission under irradiation of UV light, 365 nm. The mechanism of white light emission is attributed to effective energy transfer among fluorophores.
Coordination networks that reversibly switch between closed and open phases are of topical interest since their stepped isotherms can offer higher working capacities for gas‐storage applications than ...the related rigid porous coordination networks. To be of practical utility, the pressures at which switching occurs, the gate‐opening and gate‐closing pressures, must lie between the storage and delivery pressures. Here we study the effect of linker substitution to fine‐tune gate‐opening and gate‐closing pressure. Specifically, three variants of a previously reported pcu‐topology MOF, X‐pcu‐5‐Zn, have been prepared: X‐pcu‐6‐Zn, 6=1,2‐bis(4‐pyridyl)ethane (bpe), X‐pcu‐7‐Zn, 7=1,2‐bis(4‐pyridyl)acetylene (bpa), and X‐pcu‐8‐Zn, 8=4,4′‐azopyridine (apy). Each exhibited switching isotherms but at different gate‐opening pressures. The N2, CO2, C2H2, and C2H4 adsorption isotherms consistently indicated that the most flexible dipyridyl organic linker, 6, afforded lower gate‐opening and gate‐closing pressures. This simple design principle enables a rational control of the switching behavior in adsorbent materials.
Pillars of adsorption: Pillar substitution enables the fine‐tuning of the gate‐opening/gate‐closing pressures for a family of flexible coordination networks. The fact that linker flexibility favors lower gate‐opening pressure has broad implications for controlling a key parameter of switching adsorbent materials.
Closed-to-open structural transformations in flexible coordination networks are of potential utility in gas storage and separation. Herein, we report the first example of a flexible SiF6 2–-pillared ...square grid material, Cu(SiF6)(L)2 n (L = 1,4-bis(1-imidazolyl)benzene), SIFSIX-23-Cu. SIFSIX-23-Cu exhibits reversible switching between nonporous (β1) and several porous (α, γ1, γ2, and γ3) phases triggered by exposure to N2, CO2, or H2O. In addition, heating β1 to 433 K resulted in irreversible transformation to a closed polymorph, β2. Single-crystal X-ray diffraction studies revealed that the phase transformations are enabled by rotation and geometrical contortion of L. Density functional theory calculations indicated that L exhibits a low barrier to rotation (as low as 8 kJmol–1) and a rather flat energy surface. In situ neutron powder diffraction studies provided further insight into these sorbate-induced phase changes. SIFSIX-23-Cu combines stability in water for over a year, high CO2 uptake (ca. 216 cm3/g at 195 K), and good thermal stability.
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